In vivo effects of five different fractions of thymustimulin on haematopoietic recovery of mice treated with cyclophosphamide

Thymustimulin (TP-1), a thymic extract, has been widely studied for its capacity to induce T-cell proliferation and differentiation. TP-1 has also been shown to exert a stimulatory effect on haematopoiesis both in animal models and in human beings in vivo. In the present set of experiments, we have evaluated the effects of five different fractions of TP-1 on haematopoietic recovery of mice treated with cyclophosphamide (CP), compared to TP-1 in toto. Administration of two different doses (1 and 10 mg/kg) of any of the five TP-1 fractions for 4 consecutive days, together with CP (30 mg/kg), showed that fractions No. 2 (F2), No. 4 (F4) and No. 5 (F5), but not No. 1 (F1) or No. 3 (F3), exerted a protective effect on some of the haematopoietic parameters altered by CP treatment; none of the 5 TP-1 fractions, however, showed the same activity profile as TP-1 in toto. These findings indicate that, in such an experimental model, TP-1 exerts a more complete protective effect on chemotherapy-induced myelotoxicity than any single TP-1 fraction evaluated in the present study.